Particulate materials, especially inert particulate materials such as carbon black, silca, clay, talc, and polymeric materials are employed as fluidization aids for polymerization of olefin polymers, especially sticky polymers, in fluidized bed reactors, especially gas phase fluidized bed reactors. In sticky polymers such as, for example, ethylene-propylene and ethylene-propylene-diene rubbers, carbon black is the most frequently employed particulate material. Such processes are taught, for example, in U.S. Pat. Nos. 4,994,534; 5,304,588; 5,317,036; and 5,453,471, as well as WO 95/09826 and WO 95/09827. These inert particulate materials or fluidization aids are manufactured as fine powdery cohesive solids which are then formed into beads or pellets for shipping and handling. Before they can be used in olefin polymerizations, they must be subjected to grinding, drying, purification, and/or passivation processes.
For example, carbon black is classified as a solid material and is developed initially in the form of an aerosol. For this reason, carbon black just formed has a flocculent appearance, which also gives rise to the expression "fluffy" carbon black or carbon black "fluff". The fluff form of carbon black is composed of more than 96% finely dispersed carbon with small amounts of oxygen, hydrogen, nitrogen, sulfur and traces (less than 0.5%) of organic components. The fluff form of carbon black poses difficulty in dispersing, handling, and transporting. The difficulty worsens when these processes are conducted under elevated pressures. Because of this, manufacturers of carbon blacks further process carbon black fluff to provide it to consumers in the form of dispersions, powders, beads, or pellets.
To convert carbon black fluff to beads, it is oxidatively after-treated. This after-treatment can produce carbon black beads containing up to 15% oxygen. After-treated carbon black typically contains higher amounts of other contaminants (e.g., hydrogen nitrogen, sulfur, moisture). Before carbon black beads are utilized in a polymerization process to produce polymers, the polymer manufacturer subjects them to a grinding process which in turn can introduce additional impurities such as moisture and traces of metals into the ground carbon black powder so produced. The polymer manufacturer uses carbon black powder in polymerization because it is a better fluidization aid than beads.
As those skilled in the art know, oxygen, moisture (water), as well as the other above-mentioned impurities (e.g., sulfur) found in carbon black or introduced in after-treatments, are considered to be poisons in polymerization processes such as those used to produce sticky polymers. The presence of these impurities in carbon black requires extensive drying and/or purifying and passivation operations before polymerization is initiated and/or the use of a scavenger material (typically, additional amounts of co-catalyst, e.g., aluminum-alkyls halides and/or hydrides), both of which are extremely costly steps in polymer production.
It would be desirable to efficiently utilize the fine, powdery form of a particulate material, especially the fluff form of carbon black, directly in a fluidized polymerization vessel. The feeding of particulate materials, especially inert particulate materials, such as carbon black fluff from a carbon black reactor directly to a fluidized reactor would eliminate the need for most, if not all, of the after-treatment provided by the supplier of carbon black, eliminate the need for grinding carbon black beads into powder by the polymer manufacturer, and reduce the amount of co-catalyst/scavenger material or passivation agent used in the polymerization by that amount which serves as a scavenger for impurities introduced by after-treatment and grinding. In addition, as compared to beads and powder, the smaller-sized carbon black fluff would improve fluidization in the polymerizing reactor, minimize or eliminate gel formation, and enhance overall reactor operability.